DVD discs feature one or two data layers readable from one or two sides of the disc. The majority of pre-recorded DVD discs feature two data layers: single-layer discs where the data layers are singularly read from one side (DVD5) or both sides (DVD10) of the disc and dual-layer discs (DVD9) where two data layers are read from one side of the disc.
Referring to FIG. 1 there is shown a cross-section of a DVD5 type disc. For such a disc, DVD data is recorded on a portion 11 of data Layer 0 with lead-in data 10 and lead out data 12 recorded on either end thereof. A cross-section of a DVD9 type disc is shown in FIG. 2. For the DVD9 disc DVD data is recorded on portions 21 of data Layer 0 and data Layer 1. Lead in data 20 is recorded on data Layer 0 and lead out data 22 is recorded on data Layer 1.
DVD9 discs typically feature one volume or title described by the disc's “Control Data” which acts as a table of contents or description of the disc. DVD10 discs allow two separate disc volumes to be created on one disc, each readable separately and discretely by turning the disc over in a drive. However, single-layer discs are limited to 4.7 GB per side. If a publisher wishes to record two volumes or titles on one disc that total less than 8.5 GB but where one of the volumes is greater than 4.7 GB the current DVD technology does not accommodate this.